Download Unit 3 Lesson 1 Layers of the Earth

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Grade 9 Geography of Canada - Unit 3 – Lesson 1
Layers of the Earth
The Earth is divided into three chemical layers: the core, the mantle and the
The core is composed of mostly iron and
nickel and remains very hot, even after 4.5
billion years of cooling. The core is divided
into two layers: a solid inner core and a
liquid outer core.
The middle layer of the Earth, the mantle,
is made of minerals rich in the elements
iron, magnesium, silicon, and oxygen.
The crust is rich in the elements oxygen
and silicon with lesser amounts of
aluminum, iron, magnesium, calcium,
potassium, and sodium. There are two
types of crust. Basalt is the most common
rock on Earth. Oceanic crust is made of
relatively dense rock called basalt. Continental crust is made of lower density
rocks such as andesite and granite.
The outermost layers of the
Earth can be divided by their
physical properties into
lithosphere and asthenosphere.
The lithosphere (Greek lithos =
stone) is the rigid outermost
layer made of crust and
uppermost mantle. The
lithosphere is the "plate" of the
plate tectonic theory.
The asthenosphere (Greek
asthenos = devoid of force) is
part of the mantle that flows, a
characteristic called plastic
behavior. The flow of the
asthenosphere is part of mantle
convection that plays an
important role in moving lithospheric plates.